The present invention relates generally to piezoelectric devices and, more particularly, to an apparatus and method for accurately controlling movement of a piezoelectric device under varying operating temperatures.
Piezoelectric devices alter their shape in response to an applied electric field. An electric field applied in the direction of polarization effects an expansion of the piezoelectric material in the same direction, while a voltage applied in the opposite direction of polarization will cause a contraction of the material in that same direction. Piezoelectric bending actuators, such as thermally pre-stressed bending actuators, use the xe2x80x9cbendingxe2x80x9d action of the actuator to convert electrical energy into mechanical energy.
Due to the nature of their construction, however, the performance of these devices is temperature dependent and presents a problem in applications such as an engine system where the temperature of the actuator may range from 0xc2x0 C. to 100xc2x0 C. during operation. In this wide temperature range, the position of the actuator changes as a function of applied voltage and temperature so the actuator must be temperature compensated to provide a consistent, reliable and predictable movement or displacement of the actuator in response to the input command signal.
In the past, piezoelectric actuators applied as fuel system actuators were temperature compensated by mechanical means, such as by hydraulic compensation. These mechanical methods require complex designs that add significant product cost and decrease the reliability of the valve control system.
Thus, there is a need for a piezoelectric actuator that eliminates the need for complex and unreliable mechanical devices to provide temperature compensation of the actuator. There is also a need for a piezoelectric actuator that may be accurately and reliably driven to a desired position in a relatively wide temperature range of the actuator.
While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, a control system for temperature compensating a piezoelectric device includes a temperature compensating circuit that is operable to receive a control signal from a control signal source that corresponds to a desired position of the piezoelectric device. The temperature control circuit is operable to generate a temperature corrected or compensated control signal in response to an estimated temperature proximate the piezoelectric device. A piezoelectric control circuit is coupled to the temperature compensating circuit and operable to generate a control signal in response to the control signal generated by the temperature control circuit to drive the piezoelectric device to the desired position in response to the estimated temperature of the piezoelectric device.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.